The invention refers to a sole for shoes consisting of at least one substantially rigid rear portion and a flexible front portion connected with said rear portion approximately at the area of the ball of the foot. In the following the term "sole" is to comprise shoe soles of any kind such as running soles, intermediate soles, plateau soles, foot bed soles, welts, covering welts and insoles loosely to be inserted into a shoe, but also combinations of these soles as for example a combination of a welt, of an intermediate sole and of a running sole.
Known rigid soles have the advantage to support the foot in an orthopaedically favourable manner. A suitable material for rigid soles is wood, laminated wood or compressed wood included, but also cork, leather fibre materials and synthetic plastics materials can be used if they have the required strength.
It is a drawback of such completely rigid and thus not bendable soles that the stiffness of the soles at the area of the ball of the foot represents a hindrance for the rolling movement of the foot on walking and that this stiffness can, under circumstances, also be detrimental to health. For the purpose of avoiding this drawback there have already been proposed soles consisting of a substantial rigid rear portion and of a flexible front portion connected with said rear portion approximately at the area of the ball of the foot. With known soles of this type it is, however, difficult to provide a permanent connection between the substantially rigid rear portion and the flexible front portion because it is just this connecting area which is, when using shoes provided with such soles, subjected to continuous bending stresses. It has been found that usual glued connections do not withstand such bending stresses and that the sole does show after some time at least fissures at the connecting area and that therefore a shoe provided with such a sole becomes useless.
It is an object of the present invention to provide a sole in which a permanent or durable connection between the substantially rigid rear portion and the flexible front portion is reliably established. It is a further object of the invention to provide a sole which can be produced in a simple and inexpensive manner. It is a further object of the invention to provide a sole consisting of individual portions and having on the upper side of the sole at the connecting area neither disturbing elevations nor disturbing depressions.